This invention relates to the manufacture of semiconductor devices such that a given reverse avalance bulk breakdown voltage across a p-n junction can be accurately reproduced in the manufacturing process, and more specifically relates to a novel process for the manufacture of a zener diode wherein the reverse breakdown voltage of the device can be held within narrow tolerances during the manufacturing operation.
Processes for the manufacture of zener diodes are well known, and are described in numerous prior publications including, for example, U.S. Pat. No. 3,378,915, dated Apr. 23, 1968.
Zener diodes have an accurately defined reverse breakdown voltage and this characteristic is widely used in various electrical circuits. Zener diodes are normally sold with a given reverse voltage breakdown to within a tolerance of plus or minus 5%. Thus, the manufacturing operation must be closely controlled to avoid too high a rejection rate.
The actual breakdown voltage of a given device will be determined by the depth of the junction, and by the resistivity of the wafer materials. These characteristics in turn are controlled by the initial resistivity of the wafer, the diffusion temperature, and the diffusion time for a given diffusion system using given n-type or p-type conductivity materials. Consequently, the breakdown voltage of devices being produced will vary with changes in any of the above parameters.